Composite article

ABSTRACT

An alclad sheet product, suitable for porcelain enameling, having an aluminous metal cladding layer of 3003 alloy, for example, and an adjoining layer of an aluminum base alloy containing about 2 to 3 percent copper, up to about 0.4 percent manganese, and about 0.2 to 0.6 percent magnesium.

ilnited StatesPatent Webb Nov. 26, 1974 COMPOSITE ARTICLE 1,975,10510/1934 Keller 29/1975 1751 Invent Thomas Webb, Richmond, v 5:133:33?)311322 5221211111.... 11111111 1111133113312 [73] Assignee; ReynoldsMetals Company 3,482,951 12/1969 Hubbell 29/197.5

Richmond, Va. OTHER PUBLICATIONS [22] Fil d; 13, 1972 Metals Handbook,Vol. 1, 8th Edition, Published [63] Continuation of Ser. No. 78,276,Oct. 5, 1970,

abandoned.

[52] US. Cl. 29/1975 [51] Int. Cl B32b 15/00 [58] Field of Search29/1975 [56] References Cited UNITED STATES PATENTS 1,805,448 5/1931Frary 29/1975 1.865.089 6/1932 Dix 29/1975 Appl. No.: 316,177

Related US. Application Data 1961, American Society for Metals, p. 917.

Primary Examinerl'lyland Bizot Attorney, Agent, or Firm-Glenn, Palmer,Lyne & Gibbs ABSTRACT An alclad sheet product, suitable for porcelainenameling, having an aluminous metal cladding layer of 3003 alloy, forexample, and an adjoining layer of an aluminum base alloy containingabout 2 to 3 percent copper, up to about 0.4 percent manganese, andabout 0.2 to 0.6 percent magnesium.

7 Claims, N0 Drawings COMPOSITE ARTICLE This application is acontinuation of Ser. No. 78,276 filed On Oct. 5, 1970, now abandoned.

The present invention relates to a composite aluminous metal article,typically in sheet form, having an outer cladding layer suitable forporcelain enameling and an adjoining core layer which is susceptible tostrengthening under thermal conditions incident to porcelainizingtreatment. The composite is adapted for such uses as making coatedaluminum utensils, including those having an interior non-stick coating,and the core and cladding layers are selected to provide-improvedresistance to exfoliation and blistering.

BACKGROUND OF THE INVENTION Aluminum utensils are commonly'provided witha TFE coating on their interior cooking surfaces. Porcelain enameling isused to finish the exterior surfaces of these and other products made ofclad composites. The aluminous materials used for such purposes may be acommercial grade of aluminum (lXXX series) or a high aluminum contentalloy such as 3,003, either along or as cladding on a stronger basealloy providing greater rigidity. Two such clad composites previouslyused are 3,003 clad 7,005-type alloy and 1,100 clad 7,004-type alloy.

In these applications a cladding of 1,100 or 3,003 aluminum has beenselected primarily on the basis of its suitability for porcelainizing orTFE coating operations, while the 7,004 and 7,005 type alloys have beenchosen for their responsiveness to strengthening under thermalconditions incident to such operations. It has been found that theresulting combinations are less than ideal, however, because thesevcladding materials are not sufficiently anodic to such core alloys toprovide electrolytic protection.'Thus, in the event of a scratch orother discontinuity which allows access of corrosive food constituentsor water and other substances used for cleaning purposes, a form ofcorrosion may occur which tends to spread laterally along and throughthe core layer, resulting in exfoliation and blistering.

An object of the present invention is to provide an alclad compositeexhibiting improved resistance against such attack, while stillemploying conventional cladding materials adapted for porcelainenameling.

SUMMARY OF THE INVENTION It has been found that an alclad copper-bearingaluminum base core alloy provides improved results with respect tocorrosion resistance of the composite, in that such an alloy serves tolimit attack to minor pitting of a localized nature. In accordance withthe invention,

the cladding layer is bonded to a base layer of an alloy consistingessentially of aluminum, about 2 to 3 percent copper, up to about 0.4percent manganese, and about 0.2 to 0.6 percent magnesium by weight.This alloy may also contain the usual incidental impurities as well asminor alloying elements in customary amounts for recognized purposes,including, for example, up to about 0.8 percent silicon, 0.7 percentiron, 0.1 percent chromium, 0.25 percent zinc and 0.2 percent titanium.

The cladding may be applied on one or both surfaces of the base layer. Apreferred cladding alloy is 3,003, but other conventional aluminousmetal cladding materials are suitable, such as aluminum and highaluminum content alloys capable of affording electrolytic protection,particularly those of the IXXX and 3XXX series (Aluminum Associationdesignation).

EXAMPLE The following example illustrates the practice of the inventionand its presently preferred embodiment:

An ingot was prepared having a core composed of a copper-bearingaluminum base alloy and having 3,003 alloy cladding (10 percent) on bothsides, then rolled to 0.102" gage, blanked into suitable circles, andsubjected to thermal treatment to simulate porcelainizing and TFEcoating cycles. The core composition (alloy X2,036) in weightpercentages was:

0.50 max. Si

0.50 max. Fe 2.2-3.0 Cu 0.10-0.40 Mn 0.30-0.6 Mg 0.10 max. Cr 0.25 max.Zn 0.15 max. -Ti

. Others, each .05 max.

total 0.15 max. Balance aluminum.

For purposes of comparison, reference specimens were prepared fromconventional 3,003 clad 7,005- type alloy; Exfoliation tests (5-dayMASTMAASTS standard) were performed on annealed materials, and also onthose treated for 10 minutes at 1000F. and fan cooled (to simulateporcelaining) and for 15 minutes at 750F. and air cooled (to simulateTFE coating).

The conventional materials showed moderate to severe blistering both inannealed and heat treated condition.

In contrast, the composite materials ofv the present invention showedonly slight pitting (no blistering or exfoliation attack) in eithercondition.

A clad product of this sort is known commercially as Type 36 porcelainenameling sheet. Its core alloy X2036 was registered with the U.S.Aluminum Association on Aug. 13, 1970, by the assignee of thisapplication.

Alclad X2036 alloy in the form of such porcelain enameling sheet (PE-36)is suitable for conventional fabricating operations incident to makingvarious types -of cooking utensils, particularly pans and the likehaving a TFE non-stick coating or a porcelain enamel coating, or both,and such coatings are readily applied to a cladding surface of thecomposite sheet. The invention embraces the clad product itself, its usein making cooking utensils, and the method of applying such coatmgs.

The term Alclad is used here in the accepted sense to indicate a bondedcomposite having a layer of aluminum or corrosion-resistant aluminumalloy which is anodic to the core of structurally stronger aluminumalloy it covers, thus physically and electrolytically protecting siumand up to about 0.4 percent manganese by weight.

3. Type PE36 porcelain enameling sheet comprising an aluminum base alloycore consisting essentially of aluminum, 2.2 to 3.0 percent copper, 0.3to 0.6 percent magnesium and 0.10 to 0.40 percent manganese by weight;and a cladding of alloy 3,003 that is anodic to said core alloy andeffective cooperatively therewith to avoid exfoliation and blistering.

4. A cooking utensil made of sheet according to claim 3.

5. An article comprising a clad composite having a said cladding on bothsides of the sheet.

P0405) "UNITED STATES PA' ENT ()FFECE CER'HFLCAAE M QQRREQTWN Patent No.3,850,585 Dated Nov. 26, 1974 Invenwfls) T omas B. Webb It is certifiedthat: error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

T "E I I In col. 1 at lines 23, 26, 27, 28,31 and 66";=:- in col. 2 atlines 9 l4 and 27; in line 1 of cl aim l, in line 1 of elairh 2 in line5 of claim 3 and in line 2 of claim 5, no comma {should be pfesent inany of .the four-digit alloy designations. Thus, for

3,003" read -3003- and for "1,100" read -ll0 0-.

Signed and sealed this 18th day of February 1975.

(SEAL) Attest: I

c. MARSHALL DANN RUTH C: MASON v Commissioner 0f Patents AttestlngOfficer and Trademarks."

1. A CLAD ARTICLE HAVING A CLADDING OF 1,100 ALUMINUM ON A CORE ALLOYCONSISTING ESSENTIALLY OF ALUMINUM, ABOUT 2 TO 3 PERCENT COPPER, ABOUT0.2 TO 0.6 PERCENT MAGNESIUM AND UP TO ABOUT 0.4 PERCENT MANGANESE BYWEIGHT.
 2. A clad article having a cladding of 3,003 alloy on a corealloy consisting essentially of aluminum, about 2 to 3 percent copper,about 0.2 to 0.6 percent magnesium and up to about 0.4 percent manganeseby weight.
 3. Type PE36 porcelain enameling sheet comprising an aluminumbase alloy core consisting essentially of aluminum, 2.2 to 3.0 percentcopper, 0.3 to 0.6 percent magnesium and 0.10 to 0.40 percent manganeseby weight; and a cladding of alloy 3,003 that is anodic to said corealloy and effective cooperatively therewith to avoid exfoliation andblistering.
 4. A cooking utensil made of sheet according to claim
 3. 5.An article comprising a clad composite having a cladding layer composedof aluminum base alloy 3,003, and an adjoining core layer of an alloyconsisting essentially of aluminum, about 2.2 to 3 percent copper, about0.10 to 0.40 percent manganese and about 0.30 to 0.6 percent magnesium,by weight, with incidental elements and impurities not exceeding 0.8percent silicon, 0.7 percent iron, 0.1 percent chromium, 0.25 percentzinc and 0.2 percent titanium.
 6. The article of claim 5 in the form ofsheet.
 7. The article of claim 5 in the form of sheet, having saidcladding on both sides of the sheet.